In a letter sent to employees, Sarles says he’ll step aside in January, and that means the second largest public transportation system in America will be searching for new leadership.

Sarles came to Metro as interim general manager in 2010, before being appointed to the permanent role in 2011. Before coming to WMATA Sarles served as the executive director of New Jersey Transit.

Sarles has helmed Mertro at a time that has seen massive reinvestment in rebuilding the rail system, the expansion of the Silver Line, the procurement of new 7000 series cars and updating the bus fleet.

The announcement was made in an email to employees just moments before the wmata board meeting Wednesday afternoon.

In that email Sarles says, “My health is very good. My family continues to grow with eight grandchildren as of this month. It is time to rebalance my life more toward family, friends and pursuing activities that I have wanted to do for a long time.”

In a statement to the WMATA Board, Chair Tom Downs says that Sarles was critical in moving Metro past the 2009 Fort Totten collision.

“Under his stewardship, Metro rose from the saddest chapter in our history to a foundation of safety, performance and accountability,” said Downs.